J.A. Rioux and B. Juminer*
*Adapted from 3rd edition, Encyclopaedia of Occupational Health and Safety.
Annually millions of scorpion stings and anaphylactic reactions to insect stings may occur worldwide, causing tens of thousands of deaths in humans each year. Between 30,000 and 45,000 cases of scorpion stings are reported annually in Tunisia, causing between 35 and 100 deaths, mostly among children. Envenomation (toxic effects) is an occupational hazard for populations involved in agriculture and forestry in these regions.
Among the animals that can inflict injury on humans by the action of their venom are invertebrates, such as Arachnida (spiders, scorpions and sun spiders), Acarina (ticks and mites), Chilopoda (centipedes) and Hexapoda (bees, wasps, butterflies, and midges).
All species are venomous, but in practice only a few types produce injury in humans. Spider poisoning may be of two types:
- Cutaneous poisoning, in which the bite is followed after a few hours by oedema centred around a cyanotic mark, and then by a blister; extensive local necrosis may ensue, and healing may be slow and difficult in cases of bites from spiders of the Lycosa genus (e.g., the tarantula).
- Nerve poisoning due to the exclusively neurotoxic venom of the mygales (Latrodectus ctenus), which produces serious injury, with early onset, tetany, tremors, paralysis of the extremities and, possibly, fatal shock; this type of poisoning is relatively common amongst forestry and agricultural workers and is particularly severe in children: in the Amazonas, the venom of the “black widow” spider (Latrodectus mactans) is used for poison arrows.
Prevention. In areas where there is a danger of venomous spiders, sleeping accommodation should be provided with mosquito nets and workers should be equipped with footwear and working clothes that give adequate protection.
These arachnids have a sharp poison claw on the end of the abdomen with which they can inflict a painful sting, the seriousness of which varies according to the species, the amount of venom injected and the season (the most dangerous season being at the end of the scorpions’ hibernation period). In the Mediterranean region, South America and Mexico, the scorpion is responsible for more deaths than poisonous snakes. Many species are nocturnal and are less aggressive during the day. The most dangerous species (Buthidae) are found in arid and tropical regions; their venom is neurotropic and highly toxic. In all cases, the scorpion sting immediately produces intense local signs (acute pain, inflammation) followed by general manifestations such as tendency to fainting, salivation, sneezing, lachrymation and diarrhoea. The course in young children is often fatal. The most dangerous species are found amongst the genera Androctonus (sub-Saharan Africa), Centrurus (Mexico) and Tituus (Brazil). The scorpion will not spontaneously attack humans, and stings only when it considers itself endangered, as when trapped in a dark corner or when boots or clothes in which it has taken refuge are shaken or put on. Scorpions are highly sensitive to halogenated pesticides (e.g., DDT).
Sun spiders (Solpugida)
This order of arachnid is found chiefly in steppe and sub-desert zones such as the Sahara, Andes, Asia Minor, Mexico and Texas, and is non-venomous; nevertheless, sun spiders are extremely aggressive, may be as large as 10 cm across and have a fearsome appearance. In exceptional cases, the wounds they inflict may prove serious due to their multiplicity. Solpugids are nocturnal predators and may attack a sleeping individual.
Ticks and mites (Acarina)
Ticks are blood-sucking arachnids at all stages of their life cycle, and the “saliva” they inject through their feeding organs may have a toxic effect. Poisoning may be severe, although mainly in children (tick paralysis), and may be accompanied by reflex suppression. In exceptional cases death may ensue due to bulbar paralysis (in particular where a tick has attached itself to the scalp). Mites are haematophagic only at the larval stage, and their bite produces pruritic inflammation of the skin. The incidence of mite bites is high in tropical regions.
Treatment. Ticks should be detached after they are anaesthetized with a drop of benzene, ethyl ether or xylene. Prevention is based on the use of organophosphorus pesticide pest repellents.
Centipedes differ from millipedes (Diplopoda) in that they have only one pair of legs per body segment and that the appendages of the first body segment are poison fangs. The most dangerous species are encountered in the Philippines. Centipede venom has only a localized effect (painful oedema).
Treatment. Bites should be treated with topical applications of dilute ammonia, permanganate or hypochlorite lotions. Antihistamines may also be administered.
Insects may inject venom via the mouthparts (Simuliidae—black flies, Culicidae—mosquitoes, Phlebotomus—sandflies) or via the sting (bees, wasps, hornets, carnivorous ants). They may cause rash with their hairs (caterpillars, butterflies), or they may produce blisters by their haemolymph (Cantharidae—blister flies and Staphylinidae—rove beetles). Black fly bites produce necrotic lesions, sometimes with general disorders; mosquito bites produce diffuse pruriginous lesions. The stings of Hymenoptera (bees, etc.) produce intense local pain with erythema, oedema and, sometimes, necrosis. General accidents may result from sensitization or multiplicity of stings (shivering, nausea, dyspnoea, chilling of the extremities). Stings on the face or the tongue are particularly serious and may cause death by asphyxiation due to glottal oedema. Caterpillars and butterflies may cause generalized pruriginous skin lesions of an urticarial or oedematous type (Quincke’s oedema), sometimes accompanied by conjunctivitis. Superimposed infection is not infrequent. The venom from blister flies produces vesicular or bullous skin lesions (Poederus). There is also the danger of visceral complications (toxic nephritis). Certain insects such as Hymenoptera and caterpillars are found in all parts of the world; other suborders are more localized, however. Dangerous butterflies are found mainly in Guyana and the Central African Republic; blister flies are found in Japan, South America and Kenya; black flies live in the intertropical regions and in central Europe; sandflies are found in the Middle East.
Prevention. First level prevention includes mosquito nets and repellent and/or insecticide application. Workers who are severely exposed to insect bites can be desensitized in cases of allergy by the administration of increasingly large doses of insect body extract.